Is it possible to upgrade image from 4.0(8) to 4.0(12) from application partition using TFTP?
If we upgrade the image first in standby/Active without disconnecting from network, will that impect the production.
My worry is if there is mismatch in image version then failover will not work and both FWSM may try to become active.
what is the best method to upgrade FWSM in failover mode..?
No need to disable failover. Just follow what Magnus said. You will be just fine.
1. Load 4.0.12 onto both FWSM (copy tftp flash:image on both units)
2. Reload your Standby FWSM so it comes up running 4.0.12
3. Wait for it to synchronize failover
a. Reload your Active unit. This will cause a failover to occur and your Standby will become active.
b. issue "no fail active" on the active unit or issue "fail active" on the
standby unit. This will cause a failover to occur and your Standby will become active. Now reload the primary.
5. Both devices should now run 4.0.12 and synchronize failover